As a material for a package for a semiconductor and a heat sink material, a copper-tungsten alloy having a thermal expansion coefficient close to that of semi-conductor and a high thermal conductivity has popularly been used.
Because copper and tungsten are not mutually dissolved into a solid-solution state, the copper-tungsten alloy is manufactured by powder metallurgy. The manufacturing methods based on powder metallurgy are broadly classified into the infiltration method and the powder mixing method. The infiltration method comprises compacting and sintering tungsten powder alone to form a porous tungsten skeleton, and impregnating the resultant skeleton with molten copper. The powder mixing method comprises compacting a powder mixture prepared by mixing copper powder and tungsten powder at a prescribed ratio, and sintering the resulting mixture at a temperature of at least the melting point of copper. While a material having similar properties is available also by using molybdenum or a mixture of tungsten and molybdenum in place of tungsten which is a refractory metal, tungsten is actually employed more often.
However, the infiltration method and the powder mixing method described above have the following problems. First, the infiltration method has drawbacks in that the necessity of the infiltrating step after the sintering step results in a long production line and the swollen copper deposit on the surface after infiltration requires machining of the entire surface, thus resulting in a high manufacturing cost. The powder mixing method has problems in that, because the material is sintered at a temperature higher by 200 to 300.degree. C. than the melting point of copper, copper of a low viscosity in a liquified state excessively exudes onto the surface, resulting in an increase in surface roughness, occurrence of surface irregularities and a decrease in size accuracy. In the case of a stepped product, furthermore, leaching copper accumulates at the step corner which is thus rounded. In the powder mixing method, therefore, machining to the same order as in the infiltration method is required.
The present invention has therefore at object to provide a method of manufacturing a copper-bearing semiconductor substrate material, which solves the above-mentioned conventional problems, and which permits alleviation of a finishing operation.